An energy reduction unit is removably connectable to an external defibrillator to reduce the defibrillation energy delivered by the defibrillator to a patient. Use of the energy reduction unit is particularly suited to defibrillating pediatric patients (infants and children under 8) with an automatic or semi-automatic external defibrillator (AED). In one embodiment, the energy reduction unit includes an attenuator which partially dissipates energy produced by the AED. The attenuator is advantageously designed to present an impedance to the AED which, when connected to the patient, is approximately equal to the patient's impedance. The energy reduction unit may include a presence-detect function which enables the defibrillator to modify analysis of ECG signals to account for differences heart rhythms of pediatric and adult patients. In a second embodiment, the energy reduction unit includes an energy control modifier circuit which affects the charging operations performed internal to the AED. Other than being attached to the defibrillation equipment, the energy reduction unit does not otherwise change how an operator uses the equipment.
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3. A method of treating ventricular fibrillation in a patient by delivering defibrillation energy produced by a defibrillator to the patient, the method comprising the steps of:
determining whether the defibrillation energy delivered to the patient should be modified; and if the electrical defibrillation delivered to the patient should be modified, modifying the defibrillation energy delivered to the patient by connecting an energy modifier to the defibrillator which automatically reduces the amount of energy delivered, wherein modifying the defibrillation energy comprises modifying energy storage operations of the defibrillator by providing a mechanical signal from the energy modifier to the defibrillator.
1. A method of treating ventricular fibrillation in a pediatric patient with an electrical defibrillator calibrated for adults, the method comprising the steps of:
determining whether the pediatric patient is below a selected measurement threshold level, wherein the determining comprises comparing a linear dimension measurement of the pediatric patient to a corresponding linear dimension of the energy reduction unit; if the pediatric patient is below the selected measurement threshold level, connecting an energy reduction unit to the electrical defibrillator, wherein the energy reduction unit automatically reduces the amount of energy delivered; and delivering defibrillation energy to the pediatric patient.
2. The method of
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This is a divisional of application Ser. No. 09/113,803 filed on Jul. 9, 1998 now U.S. Pat. No. 6,134,468.
This application is a continuation-in-part of application Ser. No. 08/775,827 filed Dec. 31, 1996, now abandoned, for "Method and Apparatus for Reducing Defibrillation Energy."
This invention relates generally to a defibrillation method and apparatus, and more particularly to a method and apparatus for reducing the electrical energy delivered by an external defibrillator. "Defibrillators" include manual defibrillators, semi-automatic defibrillators and automatic defibrillators. This invention also relates to a method and apparatus for dynamically changing the operation of a defibrillator when treating a pediatric patient.
Sudden cardiac death is the leading cause of death in the United States. Most sudden cardiac death is caused by ventricular fibrillation ("VF"), in which the heart's muscle fibers contract without coordination, thereby interrupting normal blood flow to the body. The only known effective treatment for VF is electrical defibrillation, in which an electrical pulse is applied to the patient's heart. The electrical pulse must be delivered within a short time after onset of VF in order for the patient to have any reasonable chance of survival. Electrical fibrillation may also be used to treat shockable ventricular tachycardia ("VT"). Accordingly, defibrillation is the appropriate therapy for any shockable rhythm, i.e., VF or shockable VT.
One way of providing electrical defibrillation uses implantable defibrillators, which are surgically implanted in those patients having a high likelihood of experiencing VF. Implanted defibrillators typically monitor the patient's heart activity and automatically supply the requisite electrical defibrillation pulses to terminate VF. Implantable defibrillators are expensive, and are used in only a small fraction of the total population at risk for sudden cardiac death.
External defibrillators send electrical pulses to the patient's heart through electrodes applied to the patient's torso. External defibrillators are typically located and used in hospital emergency rooms, operating rooms, and emergency medical vehicles. Of the wide variety of external defibrillators currently available, automatic and semi-automatic external defibrillators (referred to collectively as "AEDs") are becoming increasingly popular because they can be used by relatively inexperienced personnel. Such AEDs are also especially lightweight, compact, and portable. AEDs are described in U.S. Pat. No. 5,607,454 to Cameron et al. entitled "Electrotherapy Method and Apparatus" and PCT Publication No. WO 94/27674 entitled "Defibrillator with Self-Test Features", the specifications of which are incorporated herein.
AEDs provide a number of advantages, including the availability of external defibrillation at locations where external defibrillation is not regularly expected, and is likely to be performed quite infrequently, such as in residences, public buildings, businesses, personal vehicles, public transportation vehicles, etc. Although operators of AEDs can expect to use an AED only very occasionally, they must nevertheless perform quickly and accurately when called upon. For this reason, AEDs automate many of the steps associated with operating external defibrillation equipment, and the operation of AEDs is intended to be simple and intuitive: AEDs are designed to minimize the number of operator decisions required.
Because AEDs have primarily been designed to treat adult VF and shockable VT, AEDs are typically not recommended for treating pediatric patients. One reason is that pediatric VF is not well documented and understood. For example, the optimal energy required for defibrillating infants and children has not yet been established--although currently available information suggests a starting dose of 2 J/kg. Additionally, the criteria used to analyze adult VF would not necessarily be appropriate for pediatric VF because of physiological differences between adults and pediatric patients. Such differences include, for example, heart rate. Finally, the protocol recommended for treating a pediatric victim of sudden cardiac arrest is different than the protocol recommended for treating an adult largely because pediatric VF is typically associated with respiratory failure. (See, Chameides et al. (Eds.) "Pediatric Advanced Life Support" (1997-1999) American Heart Assn).
As mentioned above, the use of AEDs for pediatric patients generally has not been considered, primarily because of concerns with potential operator confusion and machine complexity. When defibrillating pediatric patients, the operator must know the appropriate energy dose to deliver, which is based on the pediatric patient's weight or age. In practical terms, this means that an AED must have the necessary circuitry to accurately produce at least two energy levels (adult and child). Because the AED cannot automatically detect the presence of a pediatric patient, the AED must provide the operator with a means, such as an energy selector switch, to choose the proper energy level. It is also necessary that the AED properly analyze VF in pediatric patient. This may require the AED to be informed, via an operator action, that a pediatric patient is present in order to appropriately modify the ECG analysis to account for the differences between heart rhythms of pediatric and adult patients. The need for an operator to select an appropriate energy level, and to indicate to the AED whether a pediatric or adult patient is present, complicates both the AED design and the operator decision making process each time the AED is used. Added complexity is of particular concern for first responder AEDs which are designed for infrequent use, and are typically used by persons whose primary occupation is not lifesaving (such as police officers or flight attendants). Concerns regarding the possible consequences of such complications have outweighed any expected benefits associated with the small utilization rate of AEDs for pediatric patients. Nevertheless, the inability to effectively treat an infant or child near death is difficult to accept.
What is needed is a simple and effective way of reducing the amount of energy delivered to a pediatric patient by an AED. Additionally, what is needed is a device that lowers the defibrillator energy delivered to a pediatric patient as well as enables the defibrillator to modify its behavior to more effectively treat a pediatric patient. Additionally, what is needed is a device that enables the ECG analysis capabilities to dynamically change when the pediatric energy reduction unit is in place. Finally, what is needed is a simple and effective way of reducing the amount of energy delivered to a pediatric patient by a traditional AED, but which allows a seamless hand-off to a manual defibrillator (or an AED with manual capabilities).
A method and apparatus is provided for reducing energy delivered by an external defibrillator to a child or infant patient. An energy reduction unit is removably connectable to the defibrillator. In one embodiment, the energy reduction unit includes an attenuator which partially dissipates energy produced by the defibrillator. The attenuator may be designed to present an impedance to the AED which, when connected to the patient, is a function of the patient's impedance. The energy reduction unit may also include a presence-detect function which enables the defibrillator to modify ECG signal analysis to account for differences between heart rhythms of pediatric and adult patients. Additionally, the energy reduction unit may also change the care procedures the defibrillator prompts the rescuer to follow. In a second embodiment, the energy reduction unit includes an energy control modifier circuit which affects the charging operations performed internal to the AED. Once an operator has determined that a pediatric patient falls below a selected measurement threshold level, the operator connects the energy reduction unit to the defibrillator. All other steps performed by the operator are identical to those steps performed when defibrillating an adult.
In one embodiment, an energy reduction unit is described which is removably connectable to currently available AEDs and which provides the means for effectively treating pediatric patients with an AED, but without otherwise complicating AED design or operator interaction. The energy reduction unit reduces the amount of electrical energy delivered to a pediatric patient by an AED. As used herein, "pediatric" includes all children under the age of 8. Typically, "pediatric" is further divided into two sub-groups: "infant" (0-1 yr) and "child" (1-7 yr). In the following description, certain specific details are set forth in order to provide a thorough understanding of the preferred embodiment of the present invention. It will be clear, however, to one skilled in the art that the present invention may be practiced without these details. In other instances, well-known circuits have not been shown in detail in order not to unnecessarily obscure the description of the various embodiments of the invention. Also not presented in any detail are those well-known control signals and signal timing protocols associated with the internal operation of AEDs.
Referring to
Other than the simple placement of the energy reduction unit 50 between the AED 20 and the electrode unit 21, performing defibrillation for a pediatric patient 54 may be the same as the procedure for an adult patient 24, as outlined above in connection with FIG. 1. No additional operator procedure complexity or AED design complexity need be introduced.
When treating a pediatric patient with the energy reduction unit shown in
To appreciate some of the advantages achieved by use of the energy reduction unit 50 when defibrillating a pediatric patient, consider instead an AED designed to include an energy selector switch. In addition to increasing the complexity of the AED design, an operator of the AED would have to determine the appropriate setting of the energy selector switch each time the AED is used. In the event of operator error, an adult experiencing VF would then receive an inappropriately low energy defibrillation pulse, and the defibrillation procedure could be unsuccessful. Conversely, in the event of an operator error, a pediatric patient may receive an inappropriately high energy defibrillation pulse, with possible adverse consequences. Defibrillating a pediatric patient is unusual, and ideally it should be unnecessary to require an operator of an AED to consider the unusual case in every use of the instrument. In accordance with the present invention, the operator of an AED need only consider the steps associated with defibrillating a pediatric patient in the event that such an action is actually required. In the unusual case of defibrillating a pediatric patient, the operator performs a correspondingly unusual action--namely, connecting a pediatric-specific electrode unit and/or energy reduction unit to the AED.
When treating a pediatric patient with the energy reduction unit shown in
Alternatively, when treating a pediatric patient with the energy reduction unit shown in
When treating a pediatric patient with the energy reduction unit of
Normally, when a patient's ECG is being monitored and analyzed, the patient's equivalent circuit in series with the electrodes is a high impedance source of approximately 10 kΩ and 1 mV. When this signal is transmitted through the signal lines 62, 64, the spark gaps VSP1 and VSP2 are non-conducting and appear as an open circuit. The selected resistance values of resistors R2 and R3 are such as to have no appreciable effect on the high impedance ECG signal delivered from the patient to the ECG amplifier 28 within the AED 20 (see FIG. 2).
During defibrillation energy delivery, a high voltage is applied (e.g., approximately 1700V-2100V, more preferably 1800V). The equivalent patient circuit then appears to be of relatively low impedance, varying from approximately 50 to 125Ω with a mean of approximately 75Ω. During defibrillation, the high voltage pulse shorts spark gaps VSP1 and VSP2, thus introducing the resistor R1 as a shunt resistance. Those skilled in the art will appreciate that the spark gaps VSP1 and VSP2 function as voltage-sensitive switches, such that a high applied voltage promotes conduction therethrough. This function can be accomplished by numerous other well-known means. For example, one or more diodes may be employed which become(s) forward biased when a high voltage is applied.
It is desirable that the equivalent circuit of the patient 54 (see
In the example implementation depicted in
In another embodiment of the signal loop 66 can route a different presence-detect signal for infant and child patients, thus allowing the defibrillator to further define the ECG analysis, voice prompts or protocol.
Where the presence detect circuit is incorporated into the electrodes, a separate circuit can be provided for each electrode type (e.g., adult, child or infant). By integrally forming the presence detect circuit with the electrodes, each electrode type can actively be identified by the defibrillator.
Those skilled in the art will appreciate that a presence-detect function can be provided by transmitting any of a wide variety of signals from the energy reduction unit 50 to the AED 20. For example, an optical or other electromagnetic signal can be used. Additionally, a mechanical signal can provide the presence-detect function, such as a portion of the connector 64 extending within the AED 20 to mechanically trip a switch. Finally an ID chip may be provided that communicates with the defibrillator to identify the electrode type or the presence and type of energy reduction unit.
In addition to signaling to the microcomputer 32 that ECG analysis must be modified, the presence-detect function may itself signal to the microcomputer 32 that a reduced energy delivery is required. In this way, the energy reduction unit 50 need not include the attenuator 60 (see
Additionally, the energy reduction unit 50 can contain program memory usable by the AED to appropriately modify the patient treatment protocol. For example, circuitry block 68 may contain read-only memory that is readable by microcomputer 32 when the energy reduction unit 50 is attached to the defibrillator. In use, the microcomputer 32 would follow instructions provided by memory in circuitry block 68 in order to follow a treatment protocol other than the default program of AED 20. This has the advantage of allowing the AED's protocol of operator interactions, voice prompts, delivered treatments, ECG analysis, and other factors to be modified when an energy reduction unit is connected to the AED. Thus, as treatment evolves (for example, a new recommended protocol for treating pediatric cardiac arrest victims), the AED owner can receive the benefits of upgraded treatments automatically by obtaining relatively inexpensive accessory modules.
The operation of the energy reduction unit of
The function and interconnection of a number of circuits are described above. These circuits are known in the art, and one skilled in the art would be able to use such circuits in the described combination to practice the present invention. The internal details of these particular circuits are not part of, nor critical to, the invention, and a detailed description of the internal circuit operation need not be provided.
While certain embodiments of the invention have been described for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. For example, the use of the energy reduction unit 50 has been described in connection with automatic and semi-automatic external defibrillators. However, the present invention can be advantageously used with a wide variety of external defibrillation equipment. Also, a particular attenuator configuration has been described in detail in connection with
Leyde, Kent W., Morgan, Carlton B., Gliner, Bradford E., Jorgenson, Dawn
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